I partially tore my elbow tendon last July and now finally cleared to start to get back into tennis. It is an excellent tool as a part of re-entry to tennis after many months of physical therapy. It has much less impact on your arm than the regular ball as you try to get your arm/body to get use to tennis again :-)
At our school it is very important the safety of our students. This balls are great for the student's games during PE class and save.
Have always liked these balls for myself. I use them to hit against the garage door. My daughter likes them as well and will be swinging soon.